The invention relates to a semiconductor device with a thinned semiconductor chip and a method for producing the thinned semiconductor chip. In one embodiment, the thinned semiconductor chip has a patterned top side with contact pads and a rear side with a rear side electrode. The rear side electrode is cohesively connected to a chip pad of a circuit carrier via an electrically conductive layer.
Thinned semiconductor chips of this type are used in power electronics, in particular. After completion, for example, of a “CoolMOS” structure, the MOSFET function is arranged in the upper region of a semiconductor body, while the relatively thick substrate only represents a resistance between drain electrode on the rear side and source electrode on the top side, which disadvantageously increases the on resistance of the field effect power semiconductor device and generates heat loss.
Therefore, there is a need to come down from the original thickness of a semiconductor wafer to a thickness of the semiconductor body in which only active structures are contained. Ballast material of a semiconductor substrate is thus removed from the rear side by thinning. However, as the trend for thinning semiconductor wafers increases, the handling problems of such thinned semiconductor wafers increase. Thinned semiconductor wafers having a diameter of 30 cm and a thickness after thinning of less than 100 μm are practically no longer handleable per se as semiconductor wafers. If semiconductor wafers are additionally sawn up, as is customary, then microcracks and microdefects propagate from the sawing track in the edge regions of the semiconductor chips, and can impair the function of the semiconductor devices situated thereon and greatly reduce the usable area of a thinned semiconductor chip, or render unusable the entire semiconductor device which has a thinned semiconductor chip of this type.
Consequently, there is a need to reduce the original thickness of a semiconductor wafer of between 750 μm and 1200 μm to a thinned semiconductor wafer slice having a thickness of less than 100 μm. Furthermore, there is a need to keep the edge side defects as small as possible when separating the thinned semiconductor wafer.
Document DE 100 54 038 A1 discloses a method for separating semiconductor wafers whilst reducing the thickness of the individual pieces. Individual pieces are understood here to mean the semiconductor chips which are intended to be thinned to a predetermined thickness. For this purpose, the same document discloses an apparatus for producing such thinned semiconductor chips from plate-type bodies. The document discloses in principle completely producing the semiconductor chips on the top side of the semiconductor wafer before the semiconductor wafers are separated into individual pieces. Moreover, the document discloses that the separation operation is carried out before the thinning by grinding, and for this purpose depressions are introduced from the top side of the semiconductor wafer by sawing technology, which depressions are intended subsequently to form the edge regions of the singulated and thinned semiconductor chips.
If a surface of a semiconductor wafer has been prepared with sawing grooves in that way, it is adhesively bonded onto a carrier, so that the rear side of the semiconductor wafer is freely accessible and, with the aid of the carrier, the semiconductor wafer can then be ground thin from the rear side until the sawing grooves or depressions on the active top side of the semiconductor wafer are reached and the semiconductor wafer is thus now present in a fashion separated into individual semiconductor chips fixed on the carrier, without the thinned semiconductor wafer having to be handled.
This method and this apparatus have the disadvantage that the depressions introduced represent sawing grooves, the sawing operation from the top side of the semiconductor wafer, taking account of the defect situation in the edge regions, of the semiconductor chips being an extremely coarse process. During such a sawing process using diamond saws, a multiplicity of dislocations and other crystal defects are injected in the monocrystalline semiconductor wafer material, so that the edge side regions are unsuitable for active devices, so that the edge side regions can only accommodate contact pads which do not rely on a perfect monocrystalline crystal microstructure.
For these and other reasons, there is a need for the present invention.